Ribbon-freezing method and apparatus

ABSTRACT

A method and apparatus for improved control of ice-crystal formation in solid and semi-solid organic materials during freezing in a bath containing a cruciferous-oil slush is disclosed. Ribbon racks are used both to separate the items being frozen from each other and to efficiently distribute the items across the bath. This separation and distribution of the items in a ribbon improves control of the rate of freezing by preventing brine shock when the items are immersed in the brine and preventing cumulative localized thermal exhaustion during the freezing process. The ribbon rack freezing apparatus is adjustable to accommodate the variations in dwell times and flow rates required by different materials.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly directed to systems for thepreservation of organic material by freezing. More particularly, thepresent invention pertains to systems using fluids for freezing organicmaterials that have solid or semi-solid components.

2. Discussion of Related Art

Fish and meat products are conventionally frozen by direct contact withchilled surfaces or immersion in brines containing calcium chlorideand/or ethylene or propylene glycols, or immersion in the more expensiveliquid nitrogen or liquid carbon dioxide. These processes result a inloss of taste and texture in these products, through improper icecrystal formation during freezing. This produces an undesirableconcentration of salts in the flesh, as water crystallizes out of theflesh during freezing, and a subsequent loss of naturally-occurringflavored juices that have crystallized with the ice, upon thawing.

Portions of frozen foods that are shipped in heat-sealed plastic bagsare well-known in the food industry. The portions in these bags may bescaled for commercial restaurant use as well as for use by individualfamilies or family members. In many instances the food stuffs arevacuum-packed and ready to be heated in the bag, either in a microwaveor in boiling water, and served immediately. They are very convenientbecause they are then ready-to-eat after heating without furtherpreparation.

However, all conventional frozen foods are subject to some structuralbreakdown, breakdown caused by improper ice crystal formation in theoriginal freezing or improper maintenance of its frozen condition whilein storage. This structural breakdown is particularly objectionable inheat-sealed plastic bags containing pre-cooked, ready-to-eat foods. Forexample: a frozen casserole of cooked, tender stew meat and vegetablesrapidly turns to mush, if improperly maintained in the frozen state.Furthermore the result of this is particularly objectionable when itoccurs in individual ready-to eat portions. The ice crystals that breakup the solid structure of meat and vegetables, when the item partiallythaws and then is refrozen, may affect the food uniformly throughout thebag, damaging the entire portion because of the relatively small volumeof each portion.

Ready-to-cook meat, vegetable and fish portions, whether raw orpre-treated by superficial searing, broiling or deepfrying are even moresensitive. They are subject to particularly serious quality degradationin the initial freezing process, as well as to the hazards ofrefreezing, because a greater firmness and definition of texture isexpected from filets and steaks, than from pre-cooked, heat-and-eatfrozen foods such as stews or sauces.

In the fisheries industry, it was discovered that the addition ofcruciferous oils to conventional brines both increased the freezing rateand resulted in an increased thawing rate for fish frozen directly inbrine, as discussed in U.S. Pat. Nos. 4,654,217; 4,657,768 and4,840,035. A rapid freezing rate causes materials to freeze as a block,preventing the growth of a destructive multiplicity of ice crystals thatmacerates the texture of vegetable foodstuffs as well as flesh. Theformation of multiple ice crystals extending radially from the center ofa solid item is also believed by some to accelerate drip-related flavorlosses during thawing. The rapid thawing rate exhibited by foods frozenin such brines may also prevent a subsequent damage by preventing theformation of new, potentially destructive ice-crystal structures duringthe intervening half-frozen/half-thawed state.

The operating range mentioned in disclosures of freezing methods usingcruciferous-oil brines, -22° and -48° F. (-30° and -44.4° C.),represents the range within which various cruciferous-oil brineformulations can be maintained in the semi-liquid "slush" state. Abovethat range the brine lacks the necessary ice-crystal content and belowthat range the brines begin to become nearly solid, too stiff totransfer heat efficiently. However, we have observed that the taste aswell as the texture of flesh and other organic tissues is best preservedwhen the brine cooling it is maintained within a rather narrow range, arange about 4° F. (2.2° C.) wide, during the entire freezing process.The proper set point for this narrow operating range depends on the flowrate of the brine, the volume and cross-sectional dimensions of the itemand the quantity of heat stored in each, among other things. A too-fastflow or a too-cold brine is wasteful.

Control of brine-flow dynamics, as well as control of brine cooling andthe temperature variations within the bath 6 that are produced by thetendency to thermal layering in laminar brine flows are criticallyimportant to maintaining the brine at the surface of the food beingfrozen within this narrow range to assure that the desired type ofice-crystal formation takes place. For example, 1-inch (2.54-cm) thicksalmon steaks should be frozen in a cruciferous-oil brine flowing at 3feet/minute (0.91 meters) and maintained between -37° and -41° F.(-38.33° and -40.56° C.). In contrast, 2-inch (5.08-cm) thick tunasteaks are oilier as well as thicker, so that the brine needs to be abit colder, between -38° and -42° F. (-38.9° and -41.1° C.), but needflow only about half as fast through the bath, 1.5 to 2 feet/minute(0.46 to 0.61 meters/minute).

Basically, the interior of each block of tissue must pass must veryrapidly through the -0.5° to -5.0° C. range where the damaging icecrystals are most likely to form. The cruciferous oil brines areadvantageous for this purpose because, between -33° and -46° F. (-36.11°and -43.33° C.), they produce a conveniently fluid slush that has arelatively high specific heat, so that they are able to transfer moreheat per unit volume than other brines used for this purpose. The highspecific heat of this slush, representing a negative quantity of heatstored up during the formation of the slush ice crystals in the brine,allows these brines to resist the "shock" effect produced by the initialimmersion of large quantities of product in the brine, which results ina localized heating that temporarily "exhausts" of the brine's abilityto chill products.

On the other hand, it is also important to avoid the deterioration ofcellular structure that occurs when tissues are kept at an excessivelylow temperature. The cross-linking of molecules and loss of hydrationthat occurs in the frozen state, problems often referred to collectivelyas "freezer burn", must be minimized. Because this also tends to limithow low the temperature of the brine can be reduced to preventbrine-shock and brine-exhaustion, it further emphasizes the importanceof the high specific heat of cruciferous-oil brines.

In immersion batch-freezing systems conventionally used to freeze wholefish and cuts of raw meat, as well as vacuum-sealed ready-to-eat foodportions, ice-crystal formation is poorly controlled. Individual fish orchops, or individual food bags 2, are stacked into freezer bins or piledinto an ordinary basket 4 and dunked into a tank 5 holding a liquidnitrogen or brine bath 6, as shown in FIG. 1a. However, in these piles,the inner items freeze slower and, even in single-layer stacks, allitems 2 freeze more slowly than they would if they were less closelypacked. Furthermore, items in a pile or stack tend to freeze together,requiring separation steps that may either damage the bag or partiallydefrost the product, risking further damage to its texture and flavor.

The batch-processing basket 4, shown in FIG. 1, is conventionally3.5-feet high, 3.5-feet thick and 4-feet wide (1.07 m×1.07 m×1.22 m).Adding shelves to the baskets 4 so as to lay out one layer on eachshelf, provides space for a total of 288 lbs (130.64 kg.) of 12-ounce(34-gram) portions of food. Single layers provide a better-controlledrate of freezing by allowing the brine in the bath 6 to flow both overand under each item in the basket 4. However, these portions must stillbe loaded, unloaded and then rinsed and dried individually. This islabor-intensive and risks damage to the integrity of the bag and to thecondition of the food item itself. Also, the shelf-type separators areawkward to carry during loading and unloading, but unfrozen portions maybe difficult to load into slot-type separators and ice may form betweenthe slot and the portion during the unloading process, if the ambientair is humid, sticking the portion to the slot.

Conventional brine freezing operations dump the basket 4 of frozen itemsinto a rinse sink, to remove brine residues, and then pull the items outone-by-one to drain and dry before packaging. In each batch, all thehandling required for these processes must be completed very quickly, orunder refrigeration, to prevent thawing and consequentialrecrystallisation. The greater amount of handling required to processsmall individual portions merely adds to the need for speed. Moreover,the rinse and drying time of each item must be strictly controlled,which is impossible when using a rinse sink.

Fluid-convection and surface-conduction continuous-conveyor freezingsystems are used for longer runs of frozen products. U.S. Pat. No.5,522,227 discloses conveyor-belt system on which each item is firstcarried into a freezing brine and then drained as the item emerges fromthe brine. U.S. Pat. No. 4,531,373 discloses a contact-cooling belt thateliminates the draining step. U.S. Pat. No. 4,555,914, and the '183patent use dual-conduction in contacts between the moving items and twosurfaces cooled by brine, brine contained in both a lower steel tank andan upper flexible plastic tank and each tank provides one of the contactsurfaces.

In either batch or continuous processes, whenever brines are used, brineresidues and brine drip are both problematic. The continuous processesin U.S. Pat. No. 4,534,183 the ('183 patent) and U.S. Pat. No. 5,168,712addressed this drip and residue problem by using a steel or plastic webinterposed between the brines and material being frozen and then merelyseparating the web from the frozen item to avoid inconvenient,time-consuming rinsing 8a and drying 8b operations, used in the batchprocess shown in FIGS. 1a and 1b.

SUMMARY OF THE INVENTION

In accordance with the present invention, a ribbon enclosing a pluralityof items is fed onto a rack and supported by the rack as the ribbonmoves across a freezing tank containing a fluid. The ribbon is thenremoved from the rack and prepared for shipment.

In one embodiment the fluid is a brine and the ribbon is moved throughrinse and dry stations after being removed from the rack and beforebeing prepared for shipping. In a further embodiment, the ribbon ismoved through pulsed disinfecting light after being rinsed.

In a particular embodiment, the rack is submerged in the fluid after itis threaded with a piece of the ribbon. In a preferred embodiment therack is moved through the tank by the liquid flowing in the tank.

In one particular embodiment, the rack has several levels and each levelof the rack is threaded by a jig having respective ribbon shoes thatturn the ribbon at the end of each level in the rack to thread the nextlevel of the rack in the opposite direction. Preferably the jig alsoincludes drive means for propelling the ribbon as it travels into therack.

In accordance with another embodiment of the present invention, theribbon is moved continuously through the fluid in the same direction inone dimension while reversing direction in another dimension.

In another particular embodiment, apparatus in accordance with thepresent invention comprises a freezing tank and a rack providing avertically serpentine path for the ribbon as the ribbon moves throughthe tank. The rack is disposed in the tank so that the ribbon is coveredby a solution contained by the tank as the ribbon reverses direction.The ribbon is threaded into the serpentine path of the rack.

In another particular embodiment, apparatus in accordance with thepresent invention comprises a freezing tank and a rack having an axis ofrotation and a round cross section orthogonal to that axis of rotation.The rack is disposed in the tank so that the ribbon is covered by asolution contained by the tank as the ribbon reverses direction. Theribbon is wound in a spiral about the rack.

In a particular embodiment, the rack includes spiral support membersthat are spaced so as to suspend individual items between two supportmembers during part of the rack's rotation. In a preferred embodiment,the brine flows into the tank through said cross section of the rackparallel to the axis of rotation of the rack.

The ribbon provides improved temperature control in freezing andimproves efficiency in handling the items in the rinse, dry anddisinfect stages of the packing process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood when the detailed description ofthe preferred embodiments, given below, is considered in conjunctionwith the drawings provided, wherein:

FIGS. 1a and 1b show a prior art freezing system;

FIGS. 2a, 2b and 2c are schematic diagrams showing a batch-processself-unthreading rack received in a threading jig in accordance with afirst embodiment of the present invention, in cross section, elevationand plan view, respectively;

FIGS. 2d and 2e are schematic diagrams showing a batch-process freezingsystem in accordance with a first embodiment of the present invention;

FIG. 3a is a schematic diagram showing a continuous-process freezingsystem in accordance with the present invention; and

FIGS. 3b through 3f are schematic diagrams of ribbon racks for use inthe continuous-process freezing system shown in FIG. 3a.

In these drawings, like elements are assigned like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to FIGS. 2a and 2c a self-unthreading ribbon rack 10for a batch-process freezing system in accordance with the presentinvention provides roller guides 12 that direct a ribbon 14 containingvacuum-sealed food portions 16 across the width of the rack 10. Theroller guides 12 support the ribbon 14 at a series of different levels18 within the rack 10. A presently-preferred ribbon rack frame 11 forsupporting a batch of 32 12-ounce (34-gram) portions 16 is 12" high, 12"thick and 48" wide (0.3×0.3×1.22 meters). This rack size is particularlyadvantageous in that it can be lifted by one person without specialequipment. The rack frame 11 is also constructed as a simple frameworkof beams so as to minimize its resistance to the flow of the brine slushin the bath 6 and its tendancy to retain the slush when it is drained 8in the drain tray 30.

As shown in FIG. 2d the brine bath 6 preferably has a stainless-steelfloor 6b that separates the baskets 4 or racks 10 in the bath 6 from aplenum 6a in the bottom of the tank 5 where the brine is chilled byrefrigerant coils 6c. The brine is injected into the bath 6 by animpeller 6e at the loading end of the bath 6f, to reduce the risk ofthermal shock. To maximize heat transfer in this batch process, thevolume of flow is maximized and turbulence at entrance 6f and exit 6gfrom the bath is minimized by forcing the chilled brine to flow up intothe bath at the loading end 6f of the bath 6, and down into the plenum6a again at the unloading end 6g of the bath 6 across the entire widthof the tank through mesh plates 6d at each end of the floor 6b thatprevent the baskets 4 or racks 10 from blocking the brine flow.

In accordance with the present invention, the food portions 16 arecontained within a sixteen-foot (4.88-meter) vacuum-sealed food-gradepolypropylene ribbon 14. Thus continuous operation of the brine bathrequires only two people, one cutting and threading ribbons 14, theother removing and cleaning them 8a-8c. Furthermore, a rack this sizehas a slight buoyancy when the product is wholly immersed in the brinebath, depending on the product being frozen and the manner in which itwas prepared: boneless meat tends to be more bouyant than fish.

Each rack 10 has a pair of handles 10b that are suspended from hooks onsubstantially frictionless trolley-glides 11a. The glides 11a aresupported by one of a pair of parallel guide rails 11b. Each rack 10,guided by the rails 11b, is propelled by the brine as it flows acrossthe brine bath 6 from the workstation where the sixteen-foot lengths ofvacuum-sealed ribbon 14, as they emerge from the multivac, are threadedinto the racks 10, to the drain tray 30 where the ribbons 14 are removedfrom the racks 10. Bouyancy can be adjusted by adding a float 10c to thetop of the rack 10, if desired.

The rack 10 is loaded by inserting the rack into the loading jig 20,shown in FIG. 2b. The jig 20 provides respective turning shoes 22 at theend of each level 18 defined by the roller guides 12. The ribbon 14 isthreaded onto the roller guides 12 in the rack 10 by being pushed acrosson the roller guides 12 on the top level 18a of the rack 10 until thesixteen-foot ribbon 14 abuts the first turning shoe 22a. The turningshoe 22a redirects the ribbon 14 onto the next level 18b of the rack 10,and so on.

The jig 20 has respective rotary pins 24b that engage slots 24c in oneend of each of a plurality of drive rollers 24a in the rack 10. Thedrive rollers 24a cooperate with spring-loaded idler rollers 26 in therack 10 to propel the ribbon 14 past the shoes 22 until the lead end ofthe ribbon 14a appears at the exit slot 20a at the bottom of the jig 20.The drive rollers 24 are turned by a hand crank 28, having a handle 28aand a sprocket drive 28b, as shown in FIG. 2b. However the guide rollers24 may, alternatively, be motor driven.

The self-unthreading ribbon rack 10 of the present invention is threadedusing a combination of gravity and rotary drive. However, the rack 10 isunthreaded in a single motion, after the rack and ribboned have drained8, by merely grasping the ribbon 14 that extends from the bottom end 10dof the threaded rack 10 and pulling. The entire sixteen-foot ribbon isthen rinsed 8a, air-dried by a flow of cool ambient air 8b andirradiated 8c intact, for the sake of safe, efficient handling.

After being removed from the rack 10, each ribbon is inserted into avertical slot in a gate 56b that feeds the ribbon 14, lengthwise, into aseries of vertical guide rollers 56c where the whole ribbon 14 isprocessed in an edgewise orientation. This is particularly advantageousfor more efficient rinsing and drying 8a, 8b, but it also makesconvenient, top-down inspection of both processed surfaces possible, asdiscussed in more detail below with reference to the ribbon racks usedfor continuous-processing.

The loaded rack 10 is drained 8 by lifting it out of the brine bath 6onto a drain tray 30 that returns the brine directly to the plenum 6a,minimizing its effect on other rack being of food being frozen. Thelocation of the tray 30 over the tank, and its direct path to the plenum6a recycles 90% of the brine such as the brine 7 that otherwise is lost:dripped from the rack onto the factory floor or trapped on the ribbon 14until it is rinsed away 8a. After the draining 8 and cleaning processes8a-8c are complete, the respective portions 16 in the sixteen-footribbon 14 are turned flat again, cut apart from each other and boxed forshipment 8d.

It has been found that the ribbon-rack method and apparatus inaccordance with the present invention improves both the labor efficiencyand the temperature control needed in the food-freezing process. Theself-unthreading ribbon rack 10 in a head-to-head competition with themore conventional slot-loading rack process has proved more successfulin both these categories: labor-efficiency and freezing-rate control.

Large baskets, each containing around 288 pounds (130.64 kg) of raw fishor 12-ounce portions are conventionally used for freezing piled batchesof those food portions in a brine bath, because of the assumption thatindustrial efficiencies of scale would accrue. However, these are evenless efficient because the items must be handled individually in thecleaning process, and the finishing processes do not proceed in anorderly, continuous manner when the work crew must drop what they aredoing to help hoist a 288-pound basket, as indicated in FIG. 1b, leavingworkers further down the line intermittently without food products toprocess.

Ten smaller, shelf-loading baskets, or ten ribbon racks 10, can produce240 pounds (108.86 kg) of 12-ounce portions. Loosely packed, theshelf-baskets 4 required the same amount of freezing time as the ribbonracks 10, but twice the loading time (0.1 worker-hours) and about 50%more finishing time for rinsing, drying, treating, packing and storing(2.2 worker-hours), in contrast to the process of FIG. 2e, for a totalof 3.8 worker-hours.

Of course, the greater disadvantage of the large baskets 4 is theirperformance in the brine bath 6 itself, even when the food items aresupported on loosely-packed shelves within the basket so as to permitbrine to flow past the sides of each item. Providing an internaltemperature of -15° F. (-26.11° C.) for all 12-ounce food portions in a288-pound batch required 50 minutes for a basket where the entire288-pound batch was supported in single layers on respective shelveswithin the basket 4. In contrast, immersing one of the ribbon racks 10in the bath 6 every minute resulted in 288 pounds of 12-ounce foodportions reaching the desired -15° F. (-26.11° C.) in only 25 minutes.

The same tank was used in each case, a standard brine-bath freezing unit13 feet long by 4.5 feet wide by 46-inches deep (3.96 meters×1.37meters×116.75 centimeters). The cruciferous-oil brine in which theportions 16 were immersed was 42-inches (106.60-centimeters) deep andcooled in a plenum 6a below the bath 6 to a temperature of -40° F. (-40°C.) The brine flowed across the tank at a rate of 3 feet/minute (0.91meters/minute) floating the loaded racks toward the cleaning and packingstations 8a-8d at a rate of 1.5 feet/minute (0.46 meters/minute), abouthalf the speed of the brine. It appears that racks' slight resistance tobrine flow in itself encourages mixing across any temperaturedifferential that might otherwise form in the bath, without producinglocalized stagnation that would compromise temperature control forindividual portions 16 in the bath.

The freezing rate of the large, conventional 288-pound capacity basketsis not only slower, the lowering of such a large basket of raw fish intothe brine "shocks" the brine it contacts, reducing ice-crystal content.This reduces the overall cooling capacity of the brine passing aroundand through the basket 4, as well as locally raising its temperature,delaying the brine's return to the desired temperature range. In thehead-to-head tests, when shocked by the sudden local introduction of themassive 288-pound basket of single-layer raw salmon steaks, the brineexceeded the high-temperature limit of -37° F. (-38.33° C.) in andaround the 288-pound basket by as much as 5° F. (3° C.), shortly afterimmersion. When brine enters from the plenum 6a at a temperature of -40°F. (-40° C.), the lower limit of the desired temperature range, it willquickly become exhausted, too warm for the desired rate of freezing.Attempting to increase efficiency by freezing two 288-pound baskets inthe bath 6 quickly warms the entire bath to -34° F.

Thus, because of the thermal shock caused by the simultaneous immersionof large quantities of product into the brine bath, and because ofexcessive local temperature variations permitted by local exhaustion ofthe brine, the internal freezing rate of individual portions 16 of theproduct cannot be properly controlled when large racks or baskets used,even though the items are separated from each other within the rack toexpedite their freezing. Thus much of the texture and taste advantagesof using the complex, expensive cruciferous-oil brines are dissipatedanytime such large racks are used for batch processing.

FIG. 3a shows a continuous-process freezing system in accordance with asecond embodiment of the present invention. In this system, a continuousribbon 50 of vacuum-sealed portions 16 is supplied in batches by a"multivac"-type wrapping machine 52. The ribbon passes through acatenary 54, that provides slack to compensate for the discontinuousoutput of the wrapping machine 52, to the intake chute 56 at the top ofa pre-threaded, horizontal rotary freezing rack 58.

The rotary freezing rack 58 is threaded at the beginning of eachproduction run by winching the rack out of the brine bath 6 a wrapping aheavy mono-filament nylon line about the circumference of the rack 58 inplace of the more-expensive food-grade polypropylene ribbon material.The trailing end of the nylon line 70 is heat-sealed onto the leadingend 50a of the ribbon 50, so that the precisely-controlled freezing ofproduct can begin immediately, without false starts or discardedproduct, when the rack is returned to the brine bath and begins torotate again.

The rotary freezing rack 58 may be a simple stainless steel cylinder 58ahaving guide pins 23b extending radially from its surface to define ahelical path for the ribbon 50. It is preferably a stainless steelcylinder 58b having a longitudinal surface made up of helical planes 60,for processing tuna or salmon steaks, for example, the planes 60a are10.5 inches (26.65 cm) wide. The helical planes 60 lie orthogonal toangle α of the ribbon 50 where it contacts the rack 58b, so thatsequences of individual portions 16, each approximately 10.5-incheslong, are supported on sequences of respective individual helical planes60 about the circumference of the rack 58b, the width of each planebeing substantially equal to the length of each portion. These planes60a assure that the product that emerges from the brine will have atleast one flat surface, a geometric feature required by the design ofthe packaging used for some products.

Alternatively, the rotary freezing rack 58c is made up of a plurality ofhelical rods 60 that are 10.5-inches apart and supported by circularframes 62 that maintain a substantially cylindrical rack surface. Likethe helical planes 60, the rods 60a lie orthogonal to angle α of theribbon where it contacts the rack. In this way, individual portions 16in the ribbon 50 are suspended between respective pairs of rods 60a,which is advantageous for use with items that are not frozen flat.

For the sake of convenience, the helical planes 60 or rods 60a maydefine slightly spiral surfaces and the rack 58b, 58c may also have aslightly frustro-conical shape that narrows at the end of the brine bath6 where the ribbon 50 emerges from the brine, as shown in FIG. 3c. Thisnarrowing of the rack 58b and, consequently, the narrowing of the widthof the helical planes at that end 60b or the distance between rods (notshown) in each type of rack 58b, 58c expedites release of the ribbon 50from the rack by modifying the surface speed of that part of the rack60b and also gradually eliminating the previous congruency of the frozenitems 16 with the rifled surface of the rack 58b or 58c, for example thecongruency of the 10.5-inch length of ribbon for each salmon steaks andthe 10.5-inch widths on the helical racks 58b or 58c that support themnear the entrance guide 56a. The continuous ribbon 50 could also bethreaded along a vertical serpentine-path support frame 64a, so that theribbon passed vertically up and down through the brine along the lengthof the brine bath 6. It should be noted that, for this serpentine rack64a, the brine should flow across the tank to and from the plenum 6a ina direction perpendicular to the lengthwise movement of the ribbon 50and to the flow of the brine in the other embodiments, so that itencounters the ribbon 50 edgewise, minimizing the obstruction by theribbon of the brine flow. Thus the openings between the bath 6 and theplenum 6a must be relocated to the side walls of the bath.Alternatively, a stationary roller cage 64b made up of four or moreparallel roller bars could be provided. The ribbon 50 would then bewrapped around the cage 64b and pulled through the bath 6, as shown inFIG. 3f.

Either of these two latter devices 64a, 64b provides an edgewise,vertical ribbon path that reduces the effect on the ribbon 50 of thetemperature differential caused by thermal layering within the brinebath 6, averaging the temperature to which the ribbon 50 is exposed, andminimizes the ribbon's resistance to the flow of brine. However, thecorrosiveness of most brines make the gearing and journalling of themoving parts 12b, 24a, 26a required by both the vertical serpentine rack64a and the roller cage 64b very expensive and not very reliable.Furthermore, the helical movement of the ribbon 50 around the rollercage 64b risks distorting or breaking the ribbon 50 in someapplications. The axis of rotation 72 in the three rotary racks 58a,58b, 58c lies parallel to the flow of brine through the bath 6, to andfrom the plenum 6a. The rotary freezing racks 58 have a horizontal axisof rotation 72, driven by nylon-web belts 74 or a non-corrodible"polydrive" chain linkage.

To provide a variable dwell time, the time during which a portion 16 isimmersed in the brine as it travels along the racks 58a, 58b and 58c,the number of turns of the ribbon 50 around the racks is varied and theposition of the entrance and exit chutes 56a, 56b are moved along a lineparallel to the axis 72 of these rotary racks to maintain the properalignment for the feed angle α. Alternatively, the guide pins 23b may berepositioned along the simple cylindrical surface of the rack 58a shownin FIG. 3b.

After exiting from the brine bath 6, the ribbon 50 is turned on edge bythe exit chute 56b and is supported on edge through the draining 8,rinsing 8a and blow-drying 8b stages by vertical guide rollers 57. Afterthe ribbon is blow dried with ambient air 8b, the ribbon 50 is alsodisinfected by pulsed, high-energy lights 8c, such as those used in thePureBright™ process available from PurePulse Technologies, Inc. of SanDiego, Calif. This cleaning process removes contaminants from thesurfaces of the ribbon 50, while protecting the critical temperaturestability of its contents 16. The ribbon is then again laid flat by anidler roller 56c at the entrance to the packaging line 8d, where theribbon of frozen items is finally cut to separate the individualportions 16 and then boxed for shipment, and for storage in a store'sfreezer case where it is displayed to consumers.

The invention has been described with particular reference to apresently-preferred embodiment thereof. However, it will be apparent toone skilled in the art that variations and modifications are possiblewithin the spirit and scope of this invention. The invention is definedby the claims appended below.

What is claimed is:
 1. A method of freezing items in a bath having firstand second ends, a flow of a fluid and a depth, said method comprisingthe steps of:enclosing a plurality of the items in a ribbon; feedingsaid ribbon onto a rack; immersing the items in the bath at the firstend of the bath and moving said ribbon across the bath from the first tothe second end of the bath so that items are present in the fluid at aplurality depths at a given time; supporting said ribbon on said rackedgewise to the flow of the fluid as said ribbon moves across the bath;and removing said ribbon from said rack at the second end of the bath.2. The method of claim 1 wherein the bath contains a cruciferous brineslush.
 3. The method of claim 1 wherein said rack is floated in thebath.
 4. The method of claim 3 wherein said rack is moved through thebath by the flow of the fluid in the bath.
 5. The method of claim 1,further comprising the steps of:turning said ribbon on edge; andcleaning said ribbon on edge.
 6. The method of claim 5, furthercomprising the steps of:laying said ribbon flat; and separating saidplurality of items enclosed in said flat cleaned ribbon from each other.7. The method of claim 5 wherein said ribbon is disinfected by a pulsedlight during said cleaning step.
 8. The method of claim 5 wherein saidrack is submerged in the bath after it is threaded with a piece of theribbon.
 9. The method of claim 5 wherein said rack is placed in a trayduring said draining step, said tray being disposed for returning thefluid to the bath.
 10. The method of claim 5 further comprising the stepof cooling the fluid in a plenum.
 11. The method of claim 10 whereinsaid rack is placed in a tray during said draining step, said tray beingdisposed for returning the fluid directly to the plenum.
 12. The methodof claim 5 wherein said rack is submerged in the bath before it isthreaded with said ribbon, said rack having a first end at said firstopposing end of the bath and said rack having a second end at saidsecond opposing end of the bath.
 13. The method of claim 12 furthercomprising the steps of:heat sealing a second end of a line to a firstend of the ribbon; supporting said line on said rack in a verticallyreciprocal path with said first end of the line at said second opposingside of the rack and said second end of the line at said first end ofthe rack; immersing said rack in the bath; and moving said second end ofsaid line from said first to said second opposing end of the bath.